1. Field of the Invention
The invention relates to a guard section length detection method, and more particularly to a guard section length detection method based on the preamble signals.
2. Description of the Related Art
Compared with the conventional single carrier communication system, the OFDM communication system allocates data in several subcarriers, thus, the data transmission speed can be increased. Because the OFDM system is increasingly being used in wireless communication systems, a guard section is used to reduce inter-symbol interference (ISI). Inter-symbol interference (ISI) is a form of signal distortion that causes previously transmitted symbols to have an effect on the currently received symbol. Adding the guard section reduces ISI, however, because it does not carry information, transmission speed is also reduced. If the OFDM symbol length is NFFT points and the guard section length is NGI points, for example, the transmission rate after adding the guard section is
      N    FFT              N      FFT        +          N      GI      of the transmission rate without an added guard section. ISI can typically be prevented when the guard section is longer than the channel length and a longer guard section length decreases the transmission rate, and OFDM system performance does not improve.
Because the selection of the length of the guard interval depends on the channel condition, the guard interval length changes dynamically. For example, the IEEE 802.16 standard defines a guard section length of ¼, ⅛, 1/16 or 1/32 (hereafter referred to as a ¼ mode, ⅛ mode, 1/16 mode and 1/32 mode) of an actual OFDM symbol length, and the base station selects a proper guard section length based on the channel length and the environment. Thus, a method for synchronizing the guard section parameter between the transmitters and receivers is desirable.